The present application is related to the following additional applications, all of which are being filed concurrently herewith:
Ser. No. 08/884,895 entitled xe2x80x9cForward Compatible And Expandable High Speed Communications System and Method of Operation.xe2x80x9d
Ser. No. 08/884,979 entitled xe2x80x9cRate Adaptable Modem With Forward Compatible and Expandable Functionality and Method of Operation.xe2x80x9d
Ser. No. 08/884,957 entitled xe2x80x9cSoftware Rate Adaptable Modem With Forward Compatible and Expandable Functionality and Method of Operation.xe2x80x9d
Ser. No. 08/884,958 entitled xe2x80x9cModular Multiplicative Data Rate Modem and Method of Operation.xe2x80x9d
Ser. No. 08/884,959 entitled xe2x80x9cUser Controllable Applications Program For Rate Adaptable Modem With Forward Compatible and Expandable Functionality.xe2x80x9d
The invention relates generally to an interface between an operating system and a high-speed communications system which operates as a software modem by establishing a data link using only a selectable portion of the total available bandwidth (potential downstream data transmission) of a channel. The interface can configure the bandwidth to be used from the downstream data transmission based on either input from a user of a host processing system utilizing the data link, or alternatively, a calibration routine executed by the same host processing system.
Remote access and retrieval of data and information are becoming more desirable and common in both consumer and business environments. As data and information transfer is becoming more and more voluminous and complex, using traditional data links such as voice-band modems is too slow in speed. For example, the use of the Internet to locate and access information is increasing daily, but the retrieval of typical graphics, video, audio, and other complex data forms is generally unsatisfyingly slow using conventional voice-band modems. In fact, the slow rate of existing dial-up analog modems frustrates users, and commerce and interaction using the Internet would have been even higher were it not for the unacceptable delays associated with present day access technology. The ability to provide such desired services as video on demand, television (including HDTV), video catalogs, remote CD-ROMs, high-speed LAN access, electronic library viewing, etc., are similarly impeded by the lack of high speed connections.
Since the alternatives to copper line technology have proven unsatisfactory, solutions to the high speed access problem have been focused on improving the performance of voice band modems. Voice band modems operate at the subscriber premises end over a 3 kHz voice band lines and transmit signals through the core switching network; the phone company network treats them exactly like voice signals. These modems presently transmit up to 33.6 kbps over a 2-wire telephone line, even though the practical speed only twenty years ago was 1.2 kbps. The improvement in voice band modems over the past 20 years has resulted from significant advances in algorithms, digital signal processing, and semiconductor technology. Because such modems are limited to voice bandwidth (3.0 kHz), the rate is bound by the Shannon limit, around 30 kbps. A V0.34 modem, for example, achieves 10 bits per Hertz of bandwidth, a figure that approaches the theoretical Shannon limits.
There is a considerable amount of bandwidth available in copper lines, however, that has gone unused by voice band modems, and this is why a proposal known as Asymmetric Digital Subscriber Line (ADSL) was suggested in the industry as a high-speed protocol/connection alternative. The practical limits on data rate in conventional telephone line lengths (of 24 gauge twisted pair) vary from 1.544 Mbps for an 18,000 foot connection, to 51.840 Mbps for a 1,000 foot connection. Since a large proportion of current telephone subscribers fall within the 18,000 foot coverage range, ADSL can make the current copper wire act like a much xe2x80x9cbigger pipexe2x80x9d for sending computer bits and digital information (like movies and TV channels), while still carrying the voice traffic. For example, an ADSL modem can carry information 200 times faster than the typical voice band modem used today.
ADSL is xe2x80x9casymmetricxe2x80x9d in that more data goes downstream (to the subscriber) than upstream (back from the subscriber). The reason for this is a combination of cost, demand, and performance. For example, twisted pair wiring coupling increases with the frequency of the signal. If symmetric signals in many pairs are used within a cable, the data rate and line length become significantly limited by the coupling noise. Since the preponderance of target applications for digital subscriber services is asymmetric, asymmetric bit rate is not perceived to be a serious limitation at this time. Therefore, the ADSL standard proposes up to 6 Mbps for downstream, and up to 640 kbps for upstream. For example, video on demand, home shopping, Internet access, remote LAN access, multimedia access, and specialized PC services all feature high data rate demands downstream, to the subscriber, but relatively low data rates demands upstream. The principal advantage is that all of the high speed data operations take place in a frequency band above the voice band, leaving Plain Old Telephone Service (POTS) service independent and undisturbed, even if an ADSL modem fails. ADSL further provides an economical solution for transmission of high bandwidth information over existing copper line infrastructures.
Specifically, the proposed standard for ADSL divides the available transmission bandwidth into two parts. At the lower 4 kHz band, ordinary (POTS) is provided. The bulk of the rest bandwidth in the range from 4 kHz to about 1 MHz is for data transmission in the downstream direction, which is defined to be from the exchange to the subscriber. The upstream control channel uses a 160 kHz band in between. The signals in each channel can be extracted with an appropriate band-pass filter.
A DMT implementation of ADSL uses the entire available 1 MHz range of a copper phone line. It merely splits the signal into 255 separate channels, and each 4 kHz channel can be made to provide a bit rate up to the best present day voice band (33.6 kbs) modems. This results essentially in overall performance which is equivalent to around two hundred V0.34 modems used in parallel on the same line. Because each channel can be configured to a different bit rate according to the channel characteristics, it can be seen that DMT is inherently xe2x80x9crate-adaptivexe2x80x9d and extremely flexible for interfacing with different subscriber equipment and line conditions.
A number of problems arise, however, in attempting to implement a full scale ADSL transceiver cost-effectively.
First, to achieve this high bit rate transmission over existing telephone subscriber loops, advanced analog front end (AFE) devices, complicated digital signal processing techniques, and high speed complex digital designs are required. As a result, this pushes current technology limits and imposes both high cost and power consumption. For example, AFE devices in modem applications provide the interface between analog wave forms and digital samples for digital hardware/software processing. In high speed modem technologies such as ADSL, AFE devices need to operate at a very high sampling rate and high accuracy. For example, the DMT technology has a spectrum of 1 MHz and requires sampling above 50 MHz if a sigma-delta analog-to-digital (ADC) method is used. This thus requires the state-of-art ADC technology and imposes a high cost for end users.
Second, the time domain signal in ADSL/DMT transmissions is a summation of a large number of carriers modulated by quadrature amplitude modulation (QAM). This typically results in a large peak-to-peak deviation. As a result, even though a high speed AFE is made possible, a large dynamic range and high resolution AFE is required at the same time to minimize quantization errors.
Third, in addition to the high sampling rate and resolution requirement for ADSL AFEs, the other hardware and software in ADSL environment also needs to operate at a much higher speed than current conventional modem counterparts. For example, to implement the DMT technology in software, a custom and dedicated digital signal process (DSP) of a power of several hundred MIPS (millions instructions per second) is required to process many components such as error encoding and decoding, spectrum transforms, timing synchronization, etc. As with the AFE part of the system, this high speed requirement for the signal processing portion of ADSL also results in less flexible, high component costs.
Fourth, requiring a communications device (such as a modem) to fully support the total throughput of a standard such as ADSL may be inefficient in some cases, since many prospective users of high-speed data links may not need to use all the available bandwidth provided by such standards. It is generally more preferable therefore to permit users to throttle or scale the data throughput in a manner they can control, based on their particular application needs, hardware cost budget, etc. For example, a full-scale ADSL system may have the performance level of 200 times conventional V0.34 modems, but it is apparent that even a performance improvement of 10-20 times than present day available analog modems would be sufficient for many consumer applications, such as Internet access and similar uses. Thus, unlike conventional analog modems, which are available in various speeds varying generally from 14.4 to 56 Kbps, there are no known ADSL modems which offer scalable performance levels to users.
Fifth, in addition to the implementation challenge, the T1E1.4 ADSL standard does not specify the system interface and user model. Although various high level interface to support T1/E1, ATM, etc. have been described, system integration with high level protocols such as TCP/IP and interface with computer operating systems have not yet been defined. As a result, there is uncertainty how existing and future modem-based applications can work with the ADSL technology. For example, when users run an Internet application which sends and receives data to and from an Internet service provider (ISP), a mutually agreed protocol is required to set up a call and transfer data. Possible protocols available at various levels include ATM (asynchronous transfer mode), TCP/IP, ISDN, and current modem AT commands. Either one of these or a possibly new protocol needs to be defined to facilitate the adoption of ADSL technology.
An object of the present invention therefore is to provide a communications system which is fully compatible with high speed, rate adaptable protocols such as are used with ADSL, but which system is nevertheless implementable with simpler analog front end receiving/transmitting circuitry and is thus reduced in cost and complexity;
A further object of the present invention is to provide a communications system which is fully compatible with high speed, rate adaptable modulation protocols such as used with ADSL, but which system is nevertheless implementable with simpler digital signal processing circuitry and is thus reduced in cost and complexity;
Another objective of the present invention is to provide a method for transmitting data within a fractional, desirable portion of available bandwidth in a channel by modulating only a limited number of desirable sub-channel data carriers, so that a high speed data link can be achieved that is faster, and has reduced computation and hardware demands;
Yet a further objective of the present invention is to provide a communications system with smaller peak-to-peak deviation in the sub-channels signals, so as to reduce the dynamic range required for the front end ADC, and to minimize quantization errors.
Another objective of the present invention is to provide a high speed communications system having a data throughput that is easily controllable and expandable, so that the performance range of such system can be configured to any fractional percentage of total bandwidth available in a transmission channel, up to and including full bandwidth use of the channel;
A related objective of the present invention is to provide a high speed communications system that is modular so that forward compatible and expandable functionality can be incorporated flexibly and with a minimum of effort on the part of a user of such system;
Yet a further objective is to provide a system that is compatible with high speed protocols used in ADSL, but which is also easily adaptable to support preexisting high level data protocols, including those presently used for controlling high speed voice band modems;
A further object of the present invention is to provide a high speed communications system that self-calibrates its own performance level, based on the processing power available to such system;
Another objective of the present invention is to provide a high speed communications system that permits a user to configure the performance parameters of such system using conventional personal computer hardware, software and operating systems;
A further object of the present invention is to provide an interface between a host operating system and a high speed communications system that provide forward compatible and expandable functionality;
An additional aim of the present invention is to provide an improved system for concurrent control of conventional voice data traffic on a POTS channel, and upstream/downstream communications on separate sub-channels;
These objects and others are accomplished by providing a communications system that permits a host processing device to receive selected data within a narrow bandwidth from an upstream transciever which can and normally transmits a large bandwidth analog data transmission signal through a connected channel. A channel interface circuit AFE samples the received analog signal to generate a digital signal. Only a limited portion of the bandwidth may be sampled, thus reducing front end complexity. A digital signal processing circuit then extracts the selected data from this limited digital signal, which is significantly easier to process than a full bandwidth digital signal. Feedback information is provided back to the upstream transmitter which causes the upstream transmitter to transmit downstream data thereafter only using the limited bandwidth of the front end, and not the full bandwidth. This feedback information contains information about the channel that suggests to the upstream transmitter that the other bandwidth in the channel is unusable. In this manner, the upstream transceiver is trained to accommodate the lower rate downstream transceiver in a manner that nevertheless preserves protocol integrity.
In a preferred embodiment, the large bandwidth analog data transmission signal is comprised of a number of DMT modulated sub-channels, and an anti-aliasing filter on the front end of the the downstream transceiver ensures that only a limited number of such sub-channels are processed by a DMT signal processing core. The feedback information consists of non-zero SNR information for the selected sub-channels, and a sub-channel blackout xe2x80x9cmaskxe2x80x9d to eliminate the potential use of other sub-channels. The feedback information is sent by way of a front end transmitting circuit which transmits an upstream data transmission using a second frequency range different from the downstream transmission.
One implementation of the aforementioned high speed system is in a personal computer, so that the signal processing can be accomplished using a processor within such computer, which in a preferred embodiment is an X86 compatible processor. Another implementation of the aforementioned high speed system uses a dedicated signal processor for demodulating the selected sub-channels. This cuts down on processing overhead requirements for a host processing system incorporating the system. In such implementations the portion of the downstream data transmission to be processed for data extraction can be configured by a user of such systems, or alternatively, it can be dynamically determined based on an evaluation by the digital signal processing circuit of performance characteristics of different portions of the frequency spectrum within the bandwidth potential of the upstream transceiver.
In another variation, the data rate of a system such as described above can be increased by processing data from an additional second limited frequency bandwidth portion of the total available downstream bandwidth. In a preferred embodiment, this can be done by including a number of anti-aliasing filters in a modular bank as part of the analog front end section, each of which passes a different frequency bandwidth portion. By making the analog front end modular, the data rate of the overall system can be scaled in a controllable and cost-effective fashion. At the same time, each analog front end portion can be operated at a slower sampling clock and smaller dynamic range. This results in a more relaxed speed requirement and smaller quantization noise at a given number of bits per sample.
The present disclosure also includes an interface to an operating system, to facilitate controlling the high speed communications system when it is incorporated in a personal computer system. This interface ensures that the operating system treats such communications system essentially the same as other prior art voice band modems, and in a preferred embodiment, is a device driver for the Windows NT operating shell. Finally, the present disclosure also describes an applications program which permits a user of a personal computer to control the performance characteristics of the high speed communications system by setting certain system parameters when such system is incorporated in a personal computer system. This program includes an auto calibration routine for setting such system parameters, or alternatively a user of such program can tailor the settings subject to confirmation of the efficacy of such settings based on an evaluation of the processing power available to such user.
Although the inventions are described below in a preferred embodiment implementing the ADSL standard, it will be apparent to those skilled in the art the present invention would be beneficially used in any high speed rate-adaptable applications.
It should be noted that while some prior art devices also have limited mechanisms for achieving a reduction of nominal or peak transmission speed in a channel, they only activate or implement such mechanisms as a fallback response to a failure in the channel, or because of a transmission rate reduction in the upstream transceiver. Unlike the present invention, such prior art modems, during an initialization process, attempt to establish the highest possible transmission rate achievable by the channel and the upstream transciever. In other words, any rate reduction imposed by the downstream modem is typically considered an unintended and undesirable side effect of bad channel characteristics, and not a desirable and intentional design target as set forth in the present invention. In addition, the data rate reduction in such modems is accomplished primarily by varying the number of bits per baud (hertz) at a fixed frequency, and not by controlling the overall frequency spectrum of the downstream data transmission. Moreover, in such prior art systems, no effort is made to measure, identify or use an optimal portion of the usable bandwidth or set of transmission sub-channels. Instead, such prior art systems typically use whatever available bandwidth or sub-channels happen to be usable at that instant in time.
Similarly, while a fixed 300 baud rate downstream modem can work with an upstream 33 kbs rate modem this arrangement is also unlike the present invention. This is because, again, the bandwidth reduction in such prior art device is so large that it is considered commercially unusable by today""s standards. Furthermore, the smaller bandwidth modem is not compatible with, and does not support, the higher protocols of the higher bandwidth modem, which is also undesirable from an implementation standpoint. Stated another way, unlike the present invention, the lower end modem limitations of prior art system force the data link to be set up using a low level protocol that does not take advantage of the full capabilities of more advanced protocols.
Finally, there is no mechanism for users of either of the prior art systems noted above to expand the functionality of such modems in a controlled, flexible, and modular manner.